In recent years, the use of double pane or double profile structures has become more common in order to substantially reduce heat transfer through, e.g., window, doors, façades and other building structures. Typically, such structures include an outer metal profile or frame, an inner metal profile or frame and one or more insulating strips or struts for maintaining the inner and outer profiles or frames in a spaced relationship. In addition, such insulating strips or struts are often made of a material exhibiting low conductivity in order to substantially minimize heat transfer from a warm side to a cold side of the composite structure.
However, as discussed in U.S. Pat. No. 6,035,600, in the event that one of the metal frames is subjected to a significantly different temperature environment than the other, thermal expansion of the warmer frame results in a displacement force between the respective frames of the composite section. As a result, the composite structure may bend or flex due to relative longitudinal displacement of the respective frames. This is known in the art as a “bimetal effect”, although it is not necessary for the frames to be comprised of different metals. Rather, it only refers to the different thermal expansions of the metal frames caused, e.g., by the metal frames being at different temperatures.
Heat sources causing a unilateral temperature rise include, e.g., temperature differences between a room interior and the outside air (e.g., in winter) or incident solar radiation upon the outer frame (e.g., in summer) that causes the temperature of the outer frame to rise due to absorption of solar energy. The resulting deformation of the composite structure causes an arching that may impair the function of the window, door or façade element. U.S. Pat. No. 6,035,600 proposes an insulating rod for connecting frames that is purported to provide a slight resistance to such relative longitudinal displacement.
German Patent No. 199 56 415 C1 discloses another solution to this longitudinal displacement problem. Two longitudinal edges of an insulating profile are connected by a substantially U-shaped outer bridge. The two longitudinal edges are respectively fitted to the outer and inner metal frames of a window, door or façade element. The insulating profile is preferably made of a synthetic material, such as polyamide, polyester or polypropylene, and has a Young's modulus of greater than 2,000 N/mm2. The U-shaped bridge imparts a sheer-resistant connection between the inner and outer frames and resists relative longitudinal displacement in the event that the inner and outer frame are subjected to different temperature environments.
German Patent Publication No. 198 53 235 A1 discloses an alternate solution to this problem. In certain embodiments thereof, the insulating strip has a ladder-like structure, wherein a plurality of rungs or bars extend between respective longitudinal edges adapted to be connected to respective inner and outer metal frames of a window, door or façade. The openings between the rungs may have a circular-shape, a rectangular-shape, an oval-shape or a slot-shape. The insulating profile may be co-extruded using two materials having different hardness, such that the inner rungs exhibit an increased elasticity as compared to the longitudinal edges. This design purports to minimize or prevent bending or deflection of the two sides of the composite profile due to temperature differences. In order to prevent the penetration of moisture and/or dust through the openings, this reference recommends covering the openings with a film, a sealing tape or a dipping varnish.
An insulating strip having a metal insert embedded in plastic is also known from DE 198 18 769. This insulating strip also has openings that impart a ladder-like structure to it. The openings may be square-shaped, rectangular-shaped or substantially triangular-shaped. The openings in the metal insert are intended to reduce thermal conduction and the metal insert serves to prevent a complete failure or collapse of the insulating strip in the event of a fire.